This invention relates generally to transistors, and more specifically to improvements in a process for the fabrication of silicon transistors. Still more specifically, the invention is directed to a fabrication process designed to enhance the DC current gain h.sub.FE of the silicon transistors.
As is well known, the silicon transistors in general have a silicon oxide layer formed over the chip surface. The electrical characteristics of the transistors can be stabilized by thus covering their P-N junctions with the silicon oxide layer. However, this arrangement tends to result in the decrease in the transistor parameter h.sub.FE. This is because there exists in the interface of the silicon and the silicon oxide layer not only silicon dioxide SiO.sub.2, which is a stable form of silicon oxide, but also silicon monoxide SiO. Recombination is easy to occur due to the presence of the excess valance electrons of the silicon monoxide.
In order to overcome this defect, it has been proposed to heat the transistor chip in a hydrogenous atmosphere following the formation of the silicon oxide layer thereon. This hydrogen treatment causes the excess valence electrons of the silicon monoxide to combine with hydrogen atoms, as follows: ##EQU1## Since then less recombination takes place, the DC current gain of the silicon transistor can be approximately doubled, as later described in more detail with reference to the accompanying drawings. However, no further increase in the current gain is possible solely by the hydrogen treatment.
It is also well known that the reduction in the base width of the silicon transistor results in the increase in its DC current gain. However, the transistor with the reduced base width is susceptible to rupture at the time of secondary breakdown. Its breakdown and punch-through voltages are also lowered. This scheme is therefore not adoptable for the fabrication of transistors that are intended to operate at high voltages.